The RTEMS i386 stub in
c/src/lib/libbsp/i386/shared/comm/i386-stub.c
doesn't take advantage of some of the newer gdb remote features which
permits shorter and fewer packets.
Here is a patch which uses the 'T' response to report the registers
which gdb generally needs, and implements the 'P' request to set only
a single register. The general effect is to avoid sending all the
register contents back and forth between gdb and the stub every time
the stub stops. This also implements the 'D' request which handles
the gdb detach command, so you can cleanly quit out of the debugger
and leave the target board running.
I just happened across the sync_io support in
c/src/exec/score/cpu/unix/cpu.c
(is this documented anywhere?). That looked more useful than the
signal driven I/O I was using before, so I tried it. I ran across a
few bugs in the way it uses select.
Select changes its fd_set arguments, so you can't use global variables
for them. You have to copy them into local variables first.
If select returns -1 with errno set to EINTR, then it has not changed
any of the fd_sets. You can't start looking at them.
When clearing a descriptor, the code has the usual select off by one
error when setting sync_io_nfds.
I don't see how this code could ever have worked correctly.
I have appended a patch for the problems I found.
Please find attached a new i386ex.cfg. It has been altered to change
the files that get generated with the .nxe extension to .coff. This
change is necessary to align the file names generated by "make-exe" to
the those referred to in the GDB.HOWTO found in the
i386/shared/comm directory. It has been successfully tested on ticker (
without GDB), and base_sp( with GDB ) . I just set a breakpoint and
continue...
I noticed that in the 4.0.0-beta4a tar file, the file
c/src/lib/libbsp/i386/pc386/startup/linkcmds
was changed so that it no longer handles the .gnu.linkonce.r*
sections. The appended patch was applied to the file. I'm not sure
why. I think this patch should probably be backed out, although it's
not critical for the release.
